By : Aamarpali Puri
The NIR region is the one portion of IR region towards the visible wavelength region and ranges from 0.8mm (wave number: 12500cm-1) and goes up to 2.5 mm (wave number: 400cm-1). Near-Infrared (NIR) is the region of combination bands and overtones. Overtones are defined as simple multiples of the fundamental frequencies and occur as a consequence of anharmonicity that is deviation from simple harmonic motions because of interatomic forces and other factors within the molecule. Combination bands result when two fundamental frequencies interact and are influenced by the radiation of combined frequencies representing the fundamental frequencies. Due to presence of these frequencies hydrogenic atoms, being the lightest of all the atoms, vibrate within the NIR region, giving rise to absorptions such as N-H, O-H and C-H groups; commonly found in most food type products.
NIR spectroscopy can be used for determination of moisture, alcohol, oil, protein, fat, starch, amino acids, hydroxyl ion, film thickness, latex, total carbohydrates, nicotine, attributes like stability and internal damage etc. It can be successfully applied in the areas of baked foods, beverages, fruits, grains, dairy products, meats, flows, pharmaceuticals, paper, textiles, plastics, sugar, vegetable and petrochemicals etc. Near-Infrared region is being used extensively in the food industry for the estimation of protein and moisture in wheat (William and Norris, 1983) and to predict the total sugar content of a variety of fruit juices (Lanza and Li, 1984). Near-Infrared spectrometry (Eisen et al., 1984) is a rapid technique for estimating fat, protein and ash content of mice and other animal species from a single instrument scan. NIR spectroscopy is effective for determination of moisture, fat and protein content in the fish and other meats (Solid and Solberg, 1992; Osborne et al., 1993; Shimato et al., 2003) NIR analysis is used for the determination of cotton in polyester yarns (Blanco et al., 1994), and seed oil content and fatty acid composition in sunflower through the analysis of intact seeds, husked seeds, meal and oil (Vich, Velaso and Martinez, 1998).
In sugar industry the testing of sugarcane for pol, brix, sucrose content, invert and other common constituents have traditionally been done by a series of ICUMSA (International Commission for Uniform Methods of Sugar Analysis) and AOAC (Association of Official Agricultural Chemists) test methods. As many of these methods are time consuming, operator dependent and involve the use of hazardous reagents so Near-Infrared analysis has gained rapid acceptance as an alternative method. The various applications (Edye and Clarke, 1996) of NIR in sugar industry are analysis of raw sugar, refinery liquors, run-off syrups, remelts streams, molasses and low purity streams. Near Infrared analysis of shredded (Schaffler and Meyer, 1996) cane is being used as potential replacement for direct analysis of cane. NIR spectroscopy is used for determination of chemical composition (Brix, sugar content, purity) of molasses (Salgo, Nagy and Miko, 1998). NIR spectrophotometeric analysis is an alternative polarization method for raw sugar that uses NIR wavelengths (Player et al., 2000). NIR spectroscopic analysis has become increasingly important in the sugar industry, as the increased awareness for environmental and health topics makes desirable to avoid the clarification with lead acetate. As near infrared wavelengths specific to individual component can be identified, so it can be used for quantitative analysis of constituents of sugarcane.
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